NCERT Textbook: Light, Shadow & Reflections Notes | Study Science & Technology for UPSC CSE - UPSC

 Page 1


11
Light, Shadows and
Reflections
W
e see so many objects around
us. On the way to school we
see things like buses, cars,
cycles, trees, animals and sometimes
flowers. How do you think, we see
objects?
Think of the same places at night
time if it were completely dark. What will
you see? Suppose you go inside a
completely dark room. Are you able to
see any objects in the room?
But, when you light a candle or a
torch you can see the objects present in
the room, isn’t it? Without light, things
cannot be seen. Light helps us see
objects.
The torch bulb is an object that gives
out light of its own. The Sun, is another
familiar object that gives its own light.
During the day, its light allows us to
see objects. Objects like the sun that
give out or emit light of their own are
called luminous objects.
What about objects like a chair, a
painting or a shoe? We see these when
light from a luminous object (like the
Sun, a torch or an electric light) falls on
these and then travels towards our eye.
11.1 TRANSPARENT, OPAQUE AND
TRANSLUCENT OBJECTS
Recall our grouping objects as opaque,
transparent or translucent, in Chapter
4. If we cannot see through an object at
all, it is an opaque object. If you are
able to see clearly through an object, it
is allowing light to pass through it and
is transparent. There are some objects
through which we can see, but not very
clearly. Such objects are known as
translucent.
Activity 1
Look around yourself and collect as
many objects as you can — an eraser,
plastic scale, pen, pencil, notebook,
single sheet of paper, tracing paper or a
piece of cloth. Try to look at something
far away, through each of these objects
(Fig. 11.1). Is light from a far away object
able to travel to your eye, through any
of the objects?
Record your observations in a table
as shown in Table 11.1.
We see that a given object or material
could be transparent, translucent or
Fig. 11.1 Observing objects that do or do not
allow light to pass through them
2020-21
Page 2


11
Light, Shadows and
Reflections
W
e see so many objects around
us. On the way to school we
see things like buses, cars,
cycles, trees, animals and sometimes
flowers. How do you think, we see
objects?
Think of the same places at night
time if it were completely dark. What will
you see? Suppose you go inside a
completely dark room. Are you able to
see any objects in the room?
But, when you light a candle or a
torch you can see the objects present in
the room, isn’t it? Without light, things
cannot be seen. Light helps us see
objects.
The torch bulb is an object that gives
out light of its own. The Sun, is another
familiar object that gives its own light.
During the day, its light allows us to
see objects. Objects like the sun that
give out or emit light of their own are
called luminous objects.
What about objects like a chair, a
painting or a shoe? We see these when
light from a luminous object (like the
Sun, a torch or an electric light) falls on
these and then travels towards our eye.
11.1 TRANSPARENT, OPAQUE AND
TRANSLUCENT OBJECTS
Recall our grouping objects as opaque,
transparent or translucent, in Chapter
4. If we cannot see through an object at
all, it is an opaque object. If you are
able to see clearly through an object, it
is allowing light to pass through it and
is transparent. There are some objects
through which we can see, but not very
clearly. Such objects are known as
translucent.
Activity 1
Look around yourself and collect as
many objects as you can — an eraser,
plastic scale, pen, pencil, notebook,
single sheet of paper, tracing paper or a
piece of cloth. Try to look at something
far away, through each of these objects
(Fig. 11.1). Is light from a far away object
able to travel to your eye, through any
of the objects?
Record your observations in a table
as shown in Table 11.1.
We see that a given object or material
could be transparent, translucent or
Fig. 11.1 Observing objects that do or do not
allow light to pass through them
2020-21
108 SCIENCE
Table 11.1
l a i r e t a m / t c e j b O
t c e j b o e h t h g u o r h t w e i V
/ y l l a i t r a p / y l l u f ( e l b i s s o p
) l l a t a t o n
/ e u q a p o s i t c e j b O
/ t n e r a p s n a r t
t n e c u l s n a r t
l i c n e P
l l a b r e b b u R
r e p a p g n i t i r w f o t e e h S ? e r u s y r e v t o N
opaque depending on whether it allows
light to pass through it completely,
partially or not at all.
11.2 WHAT EXACTLY ARE SHADOWS?
Activity 2
Now, one by one hold each of the opaque
objects in the sunlight, slightly above
the ground. What do you see on the
ground? You know that the dark patch
formed by each on the ground is due
to its shadow. Sometimes you can
identify the object by looking at its
shadow (Fig. 11.2).
Spread a sheet of paper on the
ground. Hold a familiar opaque object
at some height, so that its shadow is
formed on the sheet of paper on the
ground. Ask one of your friends to draw
the outline of the shadow while you are
holding the object. Draw outlines of the
shadows of other objects in a similar
way.
Now, ask some other friends to
identify the objects from these outlines
of shadows. How many objects are they
able to identify correctly?
Do you observe your shadow in a
dark room or at night when there is no
light? Do you observe a shadow when
there is just a source of light and
nothing else, in a room? It seems we
need a source of light and an opaque
object, to see a shadow. Is there anything
else required?
Activity 3
This is an activity that you will have to
do in the dark. In the evening, go out in
an open ground with a few friends. Take
a torch and a large sheet of cardboard
with you. Hold the torch close to the
ground and shine it upwards so that its
light falls on your friend's face. You now
have a source of light that is falling on
an opaque object. If there were no trees,
building or any other object behind your
friend, would you see the shadow of
your friend's head? This does not mean
Fig. 11.2 Sometimes shadow of an object gives
an idea about its shape
2020-21
Page 3


11
Light, Shadows and
Reflections
W
e see so many objects around
us. On the way to school we
see things like buses, cars,
cycles, trees, animals and sometimes
flowers. How do you think, we see
objects?
Think of the same places at night
time if it were completely dark. What will
you see? Suppose you go inside a
completely dark room. Are you able to
see any objects in the room?
But, when you light a candle or a
torch you can see the objects present in
the room, isn’t it? Without light, things
cannot be seen. Light helps us see
objects.
The torch bulb is an object that gives
out light of its own. The Sun, is another
familiar object that gives its own light.
During the day, its light allows us to
see objects. Objects like the sun that
give out or emit light of their own are
called luminous objects.
What about objects like a chair, a
painting or a shoe? We see these when
light from a luminous object (like the
Sun, a torch or an electric light) falls on
these and then travels towards our eye.
11.1 TRANSPARENT, OPAQUE AND
TRANSLUCENT OBJECTS
Recall our grouping objects as opaque,
transparent or translucent, in Chapter
4. If we cannot see through an object at
all, it is an opaque object. If you are
able to see clearly through an object, it
is allowing light to pass through it and
is transparent. There are some objects
through which we can see, but not very
clearly. Such objects are known as
translucent.
Activity 1
Look around yourself and collect as
many objects as you can — an eraser,
plastic scale, pen, pencil, notebook,
single sheet of paper, tracing paper or a
piece of cloth. Try to look at something
far away, through each of these objects
(Fig. 11.1). Is light from a far away object
able to travel to your eye, through any
of the objects?
Record your observations in a table
as shown in Table 11.1.
We see that a given object or material
could be transparent, translucent or
Fig. 11.1 Observing objects that do or do not
allow light to pass through them
2020-21
108 SCIENCE
Table 11.1
l a i r e t a m / t c e j b O
t c e j b o e h t h g u o r h t w e i V
/ y l l a i t r a p / y l l u f ( e l b i s s o p
) l l a t a t o n
/ e u q a p o s i t c e j b O
/ t n e r a p s n a r t
t n e c u l s n a r t
l i c n e P
l l a b r e b b u R
r e p a p g n i t i r w f o t e e h S ? e r u s y r e v t o N
opaque depending on whether it allows
light to pass through it completely,
partially or not at all.
11.2 WHAT EXACTLY ARE SHADOWS?
Activity 2
Now, one by one hold each of the opaque
objects in the sunlight, slightly above
the ground. What do you see on the
ground? You know that the dark patch
formed by each on the ground is due
to its shadow. Sometimes you can
identify the object by looking at its
shadow (Fig. 11.2).
Spread a sheet of paper on the
ground. Hold a familiar opaque object
at some height, so that its shadow is
formed on the sheet of paper on the
ground. Ask one of your friends to draw
the outline of the shadow while you are
holding the object. Draw outlines of the
shadows of other objects in a similar
way.
Now, ask some other friends to
identify the objects from these outlines
of shadows. How many objects are they
able to identify correctly?
Do you observe your shadow in a
dark room or at night when there is no
light? Do you observe a shadow when
there is just a source of light and
nothing else, in a room? It seems we
need a source of light and an opaque
object, to see a shadow. Is there anything
else required?
Activity 3
This is an activity that you will have to
do in the dark. In the evening, go out in
an open ground with a few friends. Take
a torch and a large sheet of cardboard
with you. Hold the torch close to the
ground and shine it upwards so that its
light falls on your friend's face. You now
have a source of light that is falling on
an opaque object. If there were no trees,
building or any other object behind your
friend, would you see the shadow of
your friend's head? This does not mean
Fig. 11.2 Sometimes shadow of an object gives
an idea about its shape
2020-21
109 LIGHT, SHADOWS AND REFLECTIONS
that there is no shadow. After all, the
light from the torch is not able to pass
through his body to the other side.
Now, ask another friend to hold the
cardboard sheet behind your friend. Is
the shadow now seen on the cardboard
sheet (Fig. 11.3)?
Thus, the shadow can be seen only
on a screen. The ground, walls of a room,
a building, or other such surfaces act
as a screen for the shadows you observe
in everyday life.
Shadows give us some information
about shapes of objects. Sometimes,
shadows can also mislead us about the
shape of the object. In Fig. 11.4 are a few
shadows that we can create with our
hands and make-believe that they are
shadows of different animals. Have fun!
Activity 4
Place a chair in the school ground on a
sunny day. What do you observe from
the shadow of the chair?
Does the shadow give an accurate
picture of the shape of the chair? If the
chair is turned around a little, how does
the shape of the shadow change?
Take a thin notebook and look at its
shadow. Then, take a rectangular box
and look at its shadow. Do the two
shadows seem to have a similar shape?
Take flowers or other objects of
different colours and look at their
shadows. A red rose and a yellow rose,
for instance. Do the shadows look
different in colour, when the colours of
the objects are different?
Take a long box and look at its
shadow on the ground. When you move
the box around, you may see that the
size of the shadow changes. When is the
shadow of the box the shortest, when
the long side of the box is pointed
towards the Sun or when the short side
is pointing towards the Sun?
Let us use this long box, to prepare
a simple camera.
Fig. 11.3 A shadow is obtained only on a
screen
Fig 11.4 Shadows of animals hidden in your hand
2020-21
Page 4


11
Light, Shadows and
Reflections
W
e see so many objects around
us. On the way to school we
see things like buses, cars,
cycles, trees, animals and sometimes
flowers. How do you think, we see
objects?
Think of the same places at night
time if it were completely dark. What will
you see? Suppose you go inside a
completely dark room. Are you able to
see any objects in the room?
But, when you light a candle or a
torch you can see the objects present in
the room, isn’t it? Without light, things
cannot be seen. Light helps us see
objects.
The torch bulb is an object that gives
out light of its own. The Sun, is another
familiar object that gives its own light.
During the day, its light allows us to
see objects. Objects like the sun that
give out or emit light of their own are
called luminous objects.
What about objects like a chair, a
painting or a shoe? We see these when
light from a luminous object (like the
Sun, a torch or an electric light) falls on
these and then travels towards our eye.
11.1 TRANSPARENT, OPAQUE AND
TRANSLUCENT OBJECTS
Recall our grouping objects as opaque,
transparent or translucent, in Chapter
4. If we cannot see through an object at
all, it is an opaque object. If you are
able to see clearly through an object, it
is allowing light to pass through it and
is transparent. There are some objects
through which we can see, but not very
clearly. Such objects are known as
translucent.
Activity 1
Look around yourself and collect as
many objects as you can — an eraser,
plastic scale, pen, pencil, notebook,
single sheet of paper, tracing paper or a
piece of cloth. Try to look at something
far away, through each of these objects
(Fig. 11.1). Is light from a far away object
able to travel to your eye, through any
of the objects?
Record your observations in a table
as shown in Table 11.1.
We see that a given object or material
could be transparent, translucent or
Fig. 11.1 Observing objects that do or do not
allow light to pass through them
2020-21
108 SCIENCE
Table 11.1
l a i r e t a m / t c e j b O
t c e j b o e h t h g u o r h t w e i V
/ y l l a i t r a p / y l l u f ( e l b i s s o p
) l l a t a t o n
/ e u q a p o s i t c e j b O
/ t n e r a p s n a r t
t n e c u l s n a r t
l i c n e P
l l a b r e b b u R
r e p a p g n i t i r w f o t e e h S ? e r u s y r e v t o N
opaque depending on whether it allows
light to pass through it completely,
partially or not at all.
11.2 WHAT EXACTLY ARE SHADOWS?
Activity 2
Now, one by one hold each of the opaque
objects in the sunlight, slightly above
the ground. What do you see on the
ground? You know that the dark patch
formed by each on the ground is due
to its shadow. Sometimes you can
identify the object by looking at its
shadow (Fig. 11.2).
Spread a sheet of paper on the
ground. Hold a familiar opaque object
at some height, so that its shadow is
formed on the sheet of paper on the
ground. Ask one of your friends to draw
the outline of the shadow while you are
holding the object. Draw outlines of the
shadows of other objects in a similar
way.
Now, ask some other friends to
identify the objects from these outlines
of shadows. How many objects are they
able to identify correctly?
Do you observe your shadow in a
dark room or at night when there is no
light? Do you observe a shadow when
there is just a source of light and
nothing else, in a room? It seems we
need a source of light and an opaque
object, to see a shadow. Is there anything
else required?
Activity 3
This is an activity that you will have to
do in the dark. In the evening, go out in
an open ground with a few friends. Take
a torch and a large sheet of cardboard
with you. Hold the torch close to the
ground and shine it upwards so that its
light falls on your friend's face. You now
have a source of light that is falling on
an opaque object. If there were no trees,
building or any other object behind your
friend, would you see the shadow of
your friend's head? This does not mean
Fig. 11.2 Sometimes shadow of an object gives
an idea about its shape
2020-21
109 LIGHT, SHADOWS AND REFLECTIONS
that there is no shadow. After all, the
light from the torch is not able to pass
through his body to the other side.
Now, ask another friend to hold the
cardboard sheet behind your friend. Is
the shadow now seen on the cardboard
sheet (Fig. 11.3)?
Thus, the shadow can be seen only
on a screen. The ground, walls of a room,
a building, or other such surfaces act
as a screen for the shadows you observe
in everyday life.
Shadows give us some information
about shapes of objects. Sometimes,
shadows can also mislead us about the
shape of the object. In Fig. 11.4 are a few
shadows that we can create with our
hands and make-believe that they are
shadows of different animals. Have fun!
Activity 4
Place a chair in the school ground on a
sunny day. What do you observe from
the shadow of the chair?
Does the shadow give an accurate
picture of the shape of the chair? If the
chair is turned around a little, how does
the shape of the shadow change?
Take a thin notebook and look at its
shadow. Then, take a rectangular box
and look at its shadow. Do the two
shadows seem to have a similar shape?
Take flowers or other objects of
different colours and look at their
shadows. A red rose and a yellow rose,
for instance. Do the shadows look
different in colour, when the colours of
the objects are different?
Take a long box and look at its
shadow on the ground. When you move
the box around, you may see that the
size of the shadow changes. When is the
shadow of the box the shortest, when
the long side of the box is pointed
towards the Sun or when the short side
is pointing towards the Sun?
Let us use this long box, to prepare
a simple camera.
Fig. 11.3 A shadow is obtained only on a
screen
Fig 11.4 Shadows of animals hidden in your hand
2020-21
110 SCIENCE
11.3 A PINHOLE CAMERA
You might think that we need a lot of
stuff to make a camera? Not really. If we
just wish to make a simple pin hole
camera.
Activity 5
Take two boxes of cardboard such that
one can slide into another with no gap
in between them. Cut open one side of
each box. On the opposite face of the
larger box, make a small hole in the
middle [Fig. 11.5 (a)]. In the smaller box,
cut out from the middle a square with a
side of about 5 to 6 cm. Cover this open
square in the box with tracing paper
(translucent screen) [Fig. 11.5 (b)]. Slide
the smaller box inside the larger one
with the hole, in such a way that the
side with the tracing paper is inside
[Fig. 11.5 (c)]. Your pinhole camera is
ready for use.
Holding the pinhole camera look
through the open face of the smaller
box. You should use a piece of black
cloth to cover your head and the pinhole
camera. Now, try to look at some distant
objects like a tree or a building through
the pinhole camera. Make sure that the
objects you wish to look at through your
pinhole camera are in bright sun shine.
Move the smaller box forward or
backward till you get a picture on the
tracing paper pasted at the other end.
Are these pinhole images different
from their shadows?
Look through your pinhole camera
at the vehicles and people moving on
the road in bright sunlight.
Do the pictures seen in the camera
show the colours of the objects on the
other side? Are the images erect or
upside down?  Surprise, surprise!
Let us now image the Sun, with our
pinhole camera. We need a slightly
different set up for this. We just need a
large sheet of cardboard with a small
pinhole in the middle. Hold the sheet
up in the Sun and let its shadow fall on
a clear area. Do you see a small circular
image of the Sun in the middle of the
shadow of the cardboard sheet?
 Look at these pinhole images of the
Sun when an eclipse is visible from your
location. Adjust your pinhole and
screen to get a clear image before the
eclipse is to occur. Look at the image as
the eclipse begins. You will notice a part
        (a)          (b) (c)
Fig. 11.5 A sliding pin hole camera
2020-21
Page 5


11
Light, Shadows and
Reflections
W
e see so many objects around
us. On the way to school we
see things like buses, cars,
cycles, trees, animals and sometimes
flowers. How do you think, we see
objects?
Think of the same places at night
time if it were completely dark. What will
you see? Suppose you go inside a
completely dark room. Are you able to
see any objects in the room?
But, when you light a candle or a
torch you can see the objects present in
the room, isn’t it? Without light, things
cannot be seen. Light helps us see
objects.
The torch bulb is an object that gives
out light of its own. The Sun, is another
familiar object that gives its own light.
During the day, its light allows us to
see objects. Objects like the sun that
give out or emit light of their own are
called luminous objects.
What about objects like a chair, a
painting or a shoe? We see these when
light from a luminous object (like the
Sun, a torch or an electric light) falls on
these and then travels towards our eye.
11.1 TRANSPARENT, OPAQUE AND
TRANSLUCENT OBJECTS
Recall our grouping objects as opaque,
transparent or translucent, in Chapter
4. If we cannot see through an object at
all, it is an opaque object. If you are
able to see clearly through an object, it
is allowing light to pass through it and
is transparent. There are some objects
through which we can see, but not very
clearly. Such objects are known as
translucent.
Activity 1
Look around yourself and collect as
many objects as you can — an eraser,
plastic scale, pen, pencil, notebook,
single sheet of paper, tracing paper or a
piece of cloth. Try to look at something
far away, through each of these objects
(Fig. 11.1). Is light from a far away object
able to travel to your eye, through any
of the objects?
Record your observations in a table
as shown in Table 11.1.
We see that a given object or material
could be transparent, translucent or
Fig. 11.1 Observing objects that do or do not
allow light to pass through them
2020-21
108 SCIENCE
Table 11.1
l a i r e t a m / t c e j b O
t c e j b o e h t h g u o r h t w e i V
/ y l l a i t r a p / y l l u f ( e l b i s s o p
) l l a t a t o n
/ e u q a p o s i t c e j b O
/ t n e r a p s n a r t
t n e c u l s n a r t
l i c n e P
l l a b r e b b u R
r e p a p g n i t i r w f o t e e h S ? e r u s y r e v t o N
opaque depending on whether it allows
light to pass through it completely,
partially or not at all.
11.2 WHAT EXACTLY ARE SHADOWS?
Activity 2
Now, one by one hold each of the opaque
objects in the sunlight, slightly above
the ground. What do you see on the
ground? You know that the dark patch
formed by each on the ground is due
to its shadow. Sometimes you can
identify the object by looking at its
shadow (Fig. 11.2).
Spread a sheet of paper on the
ground. Hold a familiar opaque object
at some height, so that its shadow is
formed on the sheet of paper on the
ground. Ask one of your friends to draw
the outline of the shadow while you are
holding the object. Draw outlines of the
shadows of other objects in a similar
way.
Now, ask some other friends to
identify the objects from these outlines
of shadows. How many objects are they
able to identify correctly?
Do you observe your shadow in a
dark room or at night when there is no
light? Do you observe a shadow when
there is just a source of light and
nothing else, in a room? It seems we
need a source of light and an opaque
object, to see a shadow. Is there anything
else required?
Activity 3
This is an activity that you will have to
do in the dark. In the evening, go out in
an open ground with a few friends. Take
a torch and a large sheet of cardboard
with you. Hold the torch close to the
ground and shine it upwards so that its
light falls on your friend's face. You now
have a source of light that is falling on
an opaque object. If there were no trees,
building or any other object behind your
friend, would you see the shadow of
your friend's head? This does not mean
Fig. 11.2 Sometimes shadow of an object gives
an idea about its shape
2020-21
109 LIGHT, SHADOWS AND REFLECTIONS
that there is no shadow. After all, the
light from the torch is not able to pass
through his body to the other side.
Now, ask another friend to hold the
cardboard sheet behind your friend. Is
the shadow now seen on the cardboard
sheet (Fig. 11.3)?
Thus, the shadow can be seen only
on a screen. The ground, walls of a room,
a building, or other such surfaces act
as a screen for the shadows you observe
in everyday life.
Shadows give us some information
about shapes of objects. Sometimes,
shadows can also mislead us about the
shape of the object. In Fig. 11.4 are a few
shadows that we can create with our
hands and make-believe that they are
shadows of different animals. Have fun!
Activity 4
Place a chair in the school ground on a
sunny day. What do you observe from
the shadow of the chair?
Does the shadow give an accurate
picture of the shape of the chair? If the
chair is turned around a little, how does
the shape of the shadow change?
Take a thin notebook and look at its
shadow. Then, take a rectangular box
and look at its shadow. Do the two
shadows seem to have a similar shape?
Take flowers or other objects of
different colours and look at their
shadows. A red rose and a yellow rose,
for instance. Do the shadows look
different in colour, when the colours of
the objects are different?
Take a long box and look at its
shadow on the ground. When you move
the box around, you may see that the
size of the shadow changes. When is the
shadow of the box the shortest, when
the long side of the box is pointed
towards the Sun or when the short side
is pointing towards the Sun?
Let us use this long box, to prepare
a simple camera.
Fig. 11.3 A shadow is obtained only on a
screen
Fig 11.4 Shadows of animals hidden in your hand
2020-21
110 SCIENCE
11.3 A PINHOLE CAMERA
You might think that we need a lot of
stuff to make a camera? Not really. If we
just wish to make a simple pin hole
camera.
Activity 5
Take two boxes of cardboard such that
one can slide into another with no gap
in between them. Cut open one side of
each box. On the opposite face of the
larger box, make a small hole in the
middle [Fig. 11.5 (a)]. In the smaller box,
cut out from the middle a square with a
side of about 5 to 6 cm. Cover this open
square in the box with tracing paper
(translucent screen) [Fig. 11.5 (b)]. Slide
the smaller box inside the larger one
with the hole, in such a way that the
side with the tracing paper is inside
[Fig. 11.5 (c)]. Your pinhole camera is
ready for use.
Holding the pinhole camera look
through the open face of the smaller
box. You should use a piece of black
cloth to cover your head and the pinhole
camera. Now, try to look at some distant
objects like a tree or a building through
the pinhole camera. Make sure that the
objects you wish to look at through your
pinhole camera are in bright sun shine.
Move the smaller box forward or
backward till you get a picture on the
tracing paper pasted at the other end.
Are these pinhole images different
from their shadows?
Look through your pinhole camera
at the vehicles and people moving on
the road in bright sunlight.
Do the pictures seen in the camera
show the colours of the objects on the
other side? Are the images erect or
upside down?  Surprise, surprise!
Let us now image the Sun, with our
pinhole camera. We need a slightly
different set up for this. We just need a
large sheet of cardboard with a small
pinhole in the middle. Hold the sheet
up in the Sun and let its shadow fall on
a clear area. Do you see a small circular
image of the Sun in the middle of the
shadow of the cardboard sheet?
 Look at these pinhole images of the
Sun when an eclipse is visible from your
location. Adjust your pinhole and
screen to get a clear image before the
eclipse is to occur. Look at the image as
the eclipse begins. You will notice a part
        (a)          (b) (c)
Fig. 11.5 A sliding pin hole camera
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111 LIGHT, SHADOWS AND REFLECTIONS
of the image of the Sun gradually
becoming darker as the eclipse starts.
Never ever look directly at the Sun.
That could be extremely harmful for
the eyes.
There is an interesting pinhole
camera in nature. Sometimes, when we
pass under a tree covered with large
number of leaves, we notice small
patches of sunlight under it (Fig. 11.6).
These circular images are, in fact,
pinhole images of the Sun. The gaps
between the leaves, act as the pinholes.
These gaps are all kinds of irregular
shapes, but, we can see circular images
of the Sun. Try to locate images of the
Paheli has another thought. Surely,
all these results that we are seeing,
formation of shadows and pinhole
images are possible only if light moves
in a straight path?
Activity 6
Let us use a piece of a pipe or a long
rubber tube. Light a candle and fix it
on a table at one end of the room. Now
standing at the other end of the room
look at the candle through the pipe
Fig. 11.6 A natural pinhole camera. Pinhole
images of the Sun under a tree!
Sun when an eclipse occurs next. That
could be so much fun!
Boojho has this thought. We saw
upside down images of people on the
road, with our pinhole camera. What
about the images of the Sun? Did we
notice them to be upside down or
anything like that?
[Fig. 11.7 (a)]. Is the candle visible? Bend
the pipe a little while you are looking at
the candle [Fig. 11.7 (b)]. Is the candle
visible now? Turn the pipe a little to your
right or left. Can you see the candle now?
What do you conclude from this?
This suggests that light travels along
a straight line, isn’t it? That is why,
when opaque objects obstruct it, a
shadow forms.
Fig. 11.7  Looking through a pipe pointed
(a) towards and (b) a little away from a candle
(a)
(b)
2020-21